The present invention relates to a liquid crystal display device of the type used for a personal computer, a work station or the like; and, more particularly, the invention relates to a technique which is applicable to the prevention of leakage of light from a backlight unit of a liquid crystal display device.
Liquid crystal display modules of the STN (Super Twisted Nematic) type or the TFT (Thin Film Transistor) type have been widely used as display devices in notebook type personal computers or the like.
Each liquid crystal display module is constituted of a liquid crystal display panel, in which a driving circuit is arranged on a peripheral part thereof, and a backlight unit which irradiates light to the liquid crystal display panel. Such a device has been disclosed in Japanese Patent Publication No. 19474/1985 and Japanese Utility Model Laid-Open No. 22780/1992.
As one example of a liquid crystal display module of the TFT type, a liquid crystal display panel is constituted such that a filter substrate, on which color filters are formed, and a TFT substrate, on which pixel electrodes and thin film transistors (TFT) are formed, are overlapped in such a manner that opposed surfaces thereof, on which orientation films are formed, face each other in a spaced manner, and sealing members are formed around the peripheral portions of both substrates. Thereafter, a liquid crystal material is filled and sealed in the space between the two substrates.
On the other hand, a black matrix is formed on the filter substrate. This black matrix is formed in such a way that it covers the peripheries of respective pixel electrodes. Due to such a constitution, an effective display area of one pixel can be partitioned, and, hence, the profile of each pixel becomes clear, so that the contrast of the liquid crystal display device can be enhanced.
Further, this black matrix is also provided for the purpose of preventing the leakage of light which is irradiated from the backlight unit through a peripheral portion to a display surface side of the liquid crystal display panel, and so the black matrix is also formed on a region where the sealing member is formed. However, when the black matrix is formed of an organic resin, the adhesive strength between the filter substrate and the organic resin is decreased. Accordingly, for example, in a cutting step in the process of manufacture of the liquid crystal display panels, a stress is applied to a region on which the sealing member is formed, so that there has been a problem in that the black matrix is peeled off from the filter substrate in the region on which the sealing member is formed.
To cope with such a problem, for example, in Japanese Patent Laid-open No. 211473/1997 (hereinafter referred to as xe2x80x9cliterature (a)xe2x80x9d), a portion of a black matrix, which is formed on a region where a sealing member is formed, is removed so as to form a region where the black matrix and the sealing member do not overlap each other, whereby the adhesive strength is enhanced. However, in the liquid crystal display device described in the literature (a), light irradiated from a backlight unit leaks from the region where the black matrix and the sealing member do not overlap to a surface side. To deal with this problem, on a peripheral portion of a surface of the TFT substrate, on the side which does not face the liquid crystal layer, a black light shielding tape is adhered to at least the region where the black matrix and the sealing member do not overlap, whereby the leakage of light from the backlight unit is prevented.
However, the operation to apply this black light shielding tape to the glass substrate, which constitutes the TFT substrate, is performed manually for every liquid crystal display panel; and, hence, the productivity is extremely poor, thus giving rise to the problem that the additional operation pushes up the manufacturing cost of the liquid crystal display device.
The present invention has been made to solve the above-described problem of the prior art, and it is an object of the present invention to provide a technique which can reduce the manufacturing cost of a liquid crystal display device by automatically and simply forming a light shielding film provided on a peripheral portion of one substrate which constitutes a liquid crystal display element.
The above-mentioned object, other objects and novel features of the present invention will be made more apparent the following description and the attached drawings.
A summary of typical features and aspects of the invention disclosed in the present application is as follows.
That is, the present invention is applicable to a liquid crystal display device which includes a liquid crystal layer, a first substrate which has a first surface thereof with a display region on which a plurality of pixel electrodes are arranged in a matrix array, a second substrate which has a first surface thereof arranged to face the first surface of the first substrate in an opposed manner and is overlapped on the first substrate with a liquid crystal layer disposed therebetween, and a sealing member, which is disposed between the first and second substrates at peripheral portions of the first and second substrates, surrounds a region where the liquid crystal layer exists at the outside of the display region, and fixedly secures the first substrate and the second substrate.
Also, in accordance with the present invention, a light shielding film is formed on at least one side of the peripheral portion of a second surface of the first substrate, and this light shielding film is formed of a polyester-based resin to which a black pigment is added.
In accordance with the present invention, although the light shielding film is formed such that the second surface of the first substrate includes a region where the sealing member is formed, it is preferable that the light shielding film is formed on a region of the first substrate on which a polarizer is not formed.
Further, the present invention is applicable to a liquid crystal display device which includes a liquid crystal layer, a first substrate which is formed of a transparent insulation substrate and has a first surface thereof with a display region on which a plurality of pixel electrodes are arranged in a matrix array, a second substrate which is formed of a transparent insulation substrate and has a first surface thereof arranged to face the first surface of the first substrate in an opposed manner and is overlapped to the first substrate with a liquid crystal layer disposed therebetween, and a sealing member, which is disposed between the first and second substrates at peripheral portions of the first and second substrates, surrounds a region where the liquid crystal layer exists at the outside of the display region, and fixedly secures the first substrate and the second substrate. This liquid crystal display device also has an upper-side case which covers the peripheries of the first and second substrates, has an opening portion which exposes the display region and is formed of a light shielding frame. An illumination means is formed on a second-surface side of the first substrate and irradiates light, wherein the second substrate includes a black matrix formed of a light shielding film which covers the peripheries of the pixel electrodes, the black matrix partially overlaps the sealing member to cover a region between the display region and the sealing member, and a portion which does not overlap the upper-side case exists in the black matrix which is disposed in the inside of the region where the sealing member exists.
In this case, the light-shielding-film forming region which is formed on at least one side of the peripheral portions of the first substrate includes a region on a second surface of the first substrate which is not covered with the upper-side case and the black matrix.
It is preferable that the film thickness of the light shielding film is set to 40 to 120 xcexcm.
Further, according to one aspect of the present invention, the light shielding film is formed on one of the long sides of the first substrate and one of the short sides of the first substrate, while on the region of the first surface of the first substrate on which the light shielding film is formed, semiconductor chips which drive respective pixels which constitute liquid crystal display elements are mounted.
Still further, according to another aspect of the present invention, the polyester resin includes a copolymer of ethylene terephthalate and modified alkylene ether terephthalate, while the black pigment includes at least one of carbon black and metal-based black pigment.
Further, the light shielding film of the present invention is formed by coating a resin film, which includes at least a polyester-based resin and black pigment, on at least one side of a peripheral portion of a second surface of the first substrate using a dispenser method and hardening the resin film thereafter.
According to another aspect of the present invention, the resin film includes a polyester-based resin, a black pigment, a dispersing agent and a solvent, wherein the content of the solvent in the resin film amounts to 30 to 60 percent by weight.
According to still another aspect of the present invention, the solvent is methoxy butyl acetate.
According to still another aspect of the present invention, the resin film has a viscosity of 500 to 3000 mPaxc2x7s.
According to still another aspect of the present invention, at the time of coating the resin film using a dispenser method, the resin film is coated using a nozzle having a diameter of 16 to 24 G at a coating pressure of 0.05 to 0.3 Mpa and at a coating speed of 100 to 400 mm/s.
In contrast to conventional black light shielding tape, the light shielding film of the present invention can be formed on the second surface of the first substrate without interposing an adhesive agent between the light shielding film and the first substrate.
Further, with respect to the light shielding film of the present invention, the film material does not crumble in a powdery form and holds a tape-like continued state so that it becomes possible to continuously peel off the light shielding film.
Further, since the light shielding film can be made thinner than the polarizer, it becomes possible to suppress irregularities in the gap of the liquid crystal layer.